The sea, and other bodies of water, have long provided an abundant supply of food in the form of harvested fish. In recent years, due to the increase in human population and the resultant increased need for food, naturally occurring fish species have been more heavily harvested, to the extent that the populations of certain fish species have declined significantly.
Governments have tried to address the problems created by declining fish harvests and the increasing demand for fish by enacting regulations that generally limit fish harvests to maintain fish populations but that may not, in the near term, result in increased fish harvests. A market-driven method for increasing the amount of fresh fish available is to apply scientific fish-farming methods to raise fish to meet the demand. These fish-farming methods hold out the promise of a more predictable and stable fish harvest that meets market needs.
A typical prior art fish-farming pen of the type used today is essentially a tension system that is anchored to the ocean floor. In one embodiment, the pen comprises four vertical spar buoys, a substantial portion of which extend below the water. The spar buoys have damper plates coupled to the bottom that damp the vertical motion of the buoys caused by wave action. The spar buoys are arranged in a rectangular array. A box-like net is positioned within the space between the spar buoys. The upper corners of the net are connected respectively to the tops of the four spar buoys by taut lines. The bottom four corners are similarly connected to the bottom of the spar buoys by separate taut lines. Two sets of anchor lines extend outwardly and downwardly, generally in a direction away from the box net, from each of the spar buoys to maintain the taut lines under tension and to anchor the net in position. If desired, a portion of the anchor line near the spar buoys can be supported by a conventional spherical float.
While the existing fish pen described above has significant advantages over older fish pen designs, the fish pen nevertheless has significant limitations. First, the fish pen is immobile in that it must be anchored in place in order to maintain its shape and thereby retain the fish within. This lack of mobility can be a serious handicap, especially when a localized natural threat to the penned fish arises, such as when toxic plankton bloom in the vicinity and threaten to kill fish in the pen. Such toxic plankton blooms occur with some frequency off the coasts of the state of Washington, Canada, and Norway. Considering that a fish pen may contain more than 200,000 fish, each of which may have consumed a considerable quantity of fish feed, the loss of fish due to naturally occurring localized threats, such as toxic plankton, poses a serious financial risk.
In order to utilize fish pens commercially, they must be of sufficient size to enable the raising of commercially useful quantities of fish per pen. Pens of this size may generate an mount of pollution that a governmental regulatory agency may consider poses an environmental risk. Consequently, commercial fish farms are generally located where there are currents to sweep away pollutants, usually in deeper waters. These restraints on the location of commercial fish pens raise additional problems. For example, it is frequently difficult to harvest a desired quantity of fish from these large fish pens in open waters. Typically, before harvesting fish, the fish is starved for about one week to ensure a higher quality product, less subject to spoilage. With regard to harvesting, it should also be noted that even a large city can absorb a supply of only a certain quantity of fresh fish daily, without depressing prices due to a glut in the market. Thus, a fish farmer, although driven by commercial necessity to have large fish pens, would desirably wish to harvest only a fraction of the fish in each pen. Nevertheless, the fish farmer is constrained to starve all fish for one week in order to remove a proportion of good quality fish. However, if, due to weather conditions, it is not possible to harvest the desired quantity of fish after they have been starved for one week, then all the fish in the pen must be fed for their preservation. Thereafter, another one-week period of waiting must take place before a second attempt at harvesting. This not only causes uneconomical delays and financial loss, due to abandonment of scheduled harvesting plans, but also increases fish feed costs.
Whereas it is advantageous to locate fish pens in zones of water bodies where there are currents of sufficient strength to carry away pollutants and provide better oxygenation, these currents also pose a problem if they are too strong. In an immobile fish pen, the fish are required to swim constantly against the current to which they are subjected. If the currents are not too strong, then generally the exercise improves the quality of the fish stock. However, when the currents exceed a certain velocity, then the fish use an excessive amount of energy for swimming, rather than conserving the energy to build mass. Thus, the mount of nutrient supplied to the fish per pound of mass gain increases, thereby increasing costs.
There exists a need for a fish pen that can be anchored in place but that can also readily be made mobile so that it can be moved as the need arises, for instance, to avoid localized dangers posed in the water body. Further, the fish pen should be of sufficient size to allow commercial fish farming with ease of harvesting raised fish. There is also a need to minimize the mount of nutrient utilized relative to the mass gain of fish.